One band of the RF spectrum which is being increasingly used for wireless communications is the unlicensed Industrial Scientific & Medical (ISM) band at 2.4 GHz. Wireless Local Area Network (WLAN) technology, which is standardized in IEEE 802.11, operates in the ISM band. One variant of IEEE 802.11 uses a frequency-hopping spread spectrum (FHSS) technique with 1 MHz channel separation and pseudorandom hops across 79 channels. Another variant (IEEE 802.11b) uses direct sequence spread spectrum (DSSS) techniques, with 22 MHz channels. WLAN technology is widely used in offices, homes and public places to support networking between users. Wireless Personal Area Network (WPAN) technology, which is standardised in IEEE 802.15.1, is another technology which operates in the ISM band. This is a 1 Mbit/s FHSS system which uses the same 79, 1 MHz-wide channels that are used by the FHSS version of IEEE 802.11. IEEE 802.15.1 hops pseudorandomly at a nominal rate of 1600 hops/second. IEEE 802.15.1 is intended as a low power, short range (<3 m) technology for interconnecting devices such as mobile phones, portable computers and wireless handsfree headsets with fixed devices or other portable devices. One commercial implementation of IEEE 802.15.1 is known as Bluetooth™.
Since both IEEE 802.11 and IEEE 802.15.1 operate in the same 2.4 GHz unlicensed ISM frequency band, there is mutual interference between the two wireless systems which may result in severe performance degradation. The interference is of most concern with IEEE 802.11b as this uses a static channel (i.e. no frequency hopping). Factors which determine the level of interference include the separation in distance between the WLAN and WPAN devices, the amount of data traffic flowing over each of the two wireless networks, the power levels of the various devices, and the data rate of the WLAN. Also, different types of information being sent over the wireless networks have different levels of sensitivity to the interference. For example, a voice link may be more sensitive to interference than a data link being used to transfer a data file.
IEEE 802.15.2-2003 “Telecommunications and Information exchange between systems—Local and metropolitan area networks Specific Requirements—Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Bands.” describes the interference problem and provides some guidance for how WLAN and WPAN equipment can coexist. Two categories of coexistence mechanisms are proposed: collaborative and non-collaborative. Collaborative coexistence mechanisms exchange information between two wireless networks. FIG. 1 shows an example piece of equipment 100 which includes a WPAN transceiver TX1 and a WLAN transceiver TX2. Equipment 100 can be, for example, a portable computer with the WLAN supporting a connection 40 with a WLAN base station 45 and the WPAN supporting a connection 30 with a WPAN device which, in this example, is a wireless headset 35. Some of the possible sources of interference are shown: WLAN transmissions from BS 45 may interfere with reception of WPAN traffic at TX1, or WPAN transmissions from TX1 may interfere with WLAN reception at the base station 45 (path 32); WPAN transmissions from head set 35 may interfere with reception of WLAN traffic at TX2, or WLAN transmissions from TX2 may interfere with WPAN reception at the head set 35 (path 42).
One solution proposed by IEEE 802.15.2 is to provide a packet traffic arbitration (PTA) arbitration device which communicates with both the WLAN station and WPAN station and provides per-packet authorization of all transmissions. FIG. 2 shows an apparatus 100 with an arbitration device 130. Both transceivers TX1, TX2 need to request permission to transmit or receive and, in response, the arbitration device 130 will either grant or deny the permission to access the shared spectrum to transmit or receive a data packet. The recommended PTA interface between a WPAN transceiver and an arbitration device is shown in FIG. 2. It comprises four lines 151-154: RF_Request, Status, Freq and RF_Confirm.
There are limitations to the effectiveness of the existing PTA arrangement. One limitation is that the PTA arbitration device performs arbitration based on a limited amount of information, such as the priority of each station's request. It would be desirable to convey additional information between a WPAN station and a WLAN station (or an arbitrating entity), but providing additional signalling lines would increase the pin count of integrated circuits used in the WPAN and WLAN stations.